This invention is related to a method and apparatus for measuring the hydraulic conductivity, or permeability, of soil, and in particular, to a method and apparatus of the type that develops a head pressure from a column of liquid, such as water, above the soil to be tested and monitors the fall of the liquid head as the liquid soaks into the soil.
A long-felt, unfulfilled need has existed for a fast and accurate technique for measuring soil permeability. Such information is important in many industries. In agriculture, it is necessary in order to properly establish irrigation and drainage systems. In the construction industry, knowledge of soil conditions is important in establishing road drainage. In the home building industry, septic systems are located on the basis of the ability of the soil to "perk".
A conventional technique for measuring soil permeability is to dig a hole at the test site, fill it with water and monitor the time for the water to penetrate into the soil. Such a test is satisfactory for certain applications but is inherently inaccurate especially at extreme values of permeability and is very slow. If the soil is hard clay, the water may take several days to fully saturate into the soil. To improve the degree of accuracy, several techniques have been proposed. In one such technique, a column of water is established above the soil to be tested and a constant head pressure is maintained as water from the column soaks into the soil. The amount of water per unit of time that passes into the soil is measured and hydraulic conductivity is calculated from a known algorithm. While this technique provides a more accurate result than the conventional technique, it is equally slow, taking anywhere from one hour to two or three days to complete, and requires complicated calculations to arrive at a value of hydraulic conductivity. Furthermore, the value is a combined vertical and horizontal conductivity number with no means for separating the horizontal from the vertical components.